Swipe sensor methods and apparatus for capturing biometric digit data, such as fingerprints, are known. Common swipe sensor apparatus and methods typically include an M×N rectangular grid array of sensor elements. An M×N array of sensor elements may be used to capture a series of biometric data image slices representative of a digit (e.g., a finger) as the digit moves relative to the M×N sensor array in a swipe or scanning motion. For example, a digit may be swiped perpendicular to a width of the rectangular sensor array. Each sensor element may form a pixel of an image slice, where an image slice corresponds to a collection of data points formed by taking one data sample from each sensor element of the M×N grid array of sensor elements. An image slice may be recorded (stored) in memory, e.g., by recording all of these data samples as a group, and/or imaged. A series of discrete image slices may be captured at fixed time intervals and stitched together to reconstruct an image of a digit moving across the sensor array. A series of image slices may be captured before the digit moves a distance equal to the height of the sensor array, and the series of image slices then may be reconstructed to form a composite image. Such reconstruction of the series of slices may provide additional data points spatially offset among different slices so as to fill in gaps between data points of the sensor array in any given slice. Such reconstruction also may provide a final composite image larger than the M×N rectangular sensor array. Recording swipe biometric data in slices historically requires collection of sensor generated data at a fixed time interval that is limited by a maximum capture rate of the grid of sensor elements. For example, if there are N rows of pixels, and if a finger is not moved more than the distance covered by the N rows by the time the next slice is recorded, consecutive image slices may be stitched together to form a continuous, composite image larger than the M×N sensor array.
Although M×N array swipe sensors and methods have utility in many applications, such swipe sensors and methods have a drawback in that recording the data in image slices of M×N elements requires that the data be recorded (stored) and post-processed in order to reconstruct (stitch) the image slices together into a recognizable image of a fingerprint or other biometric image of the digit. Also, most M×N array swipe sensors cannot freeze the data from all sensor elements of the M×N array at one instant in time. The sensor elements of a M×N sensor array typically are sampled (digitized) sequentially, element by element, row by row. This sequential sampling takes a finite time and introduces an image skew due to the fact that a finger moves, perhaps as much as the full N lines, between the time the first sensor element of the M×N array is sampled and the time the last sensor element of the M×N array is sampled.
Therefore, a need exists for a biometric swipe sensor and data processing method that overcomes one or both of these drawbacks.